ABSTRACT: POLYCOMB REPRESSIVE COMPLEXES AS KEY REGULATORS OF HIV LATENCY AND TARGETS FOR LATENCY REVERSAL In an effort to achieve a cure for HIV, approaches to eliminate the persistent reservoir of latent HIV infection are needed. Enforced by a delicate balance of regulators of viral and cellular gene expression, the persistence of the quiescent retroviral genome is a remarkable way by which the virus ensures its stability within the host. Manipulation of viral latency to allow renewed viral expression and the potential for viral clearance is a leading strategy for HIV cure in chronically infected patients. Chemical strategies that promote reversal of viral latency by disrupting repressive epigenetic processes represent a groundbreaking step towards a clinical strategy to cure HIV. Fortuitously, the effort to epigenetically reactivate HIV proviruses has intersected with the scientific community?s interest in chromatin regulation and an increased appreciation for the role of epigenetic chemical probes in driving biological understanding of their targets. Proof of concept studies in reactivating HIV transcription via inhibition of epigenetic regulatory proteins have yielded promising results. However, many of these compounds exhibit only modest latency reversing activity, and only a limited number of chemical tools to achieve this goal are currently available. A better understanding of the landscape of epigenetic pathways that influence proviral latency, as well as novel chemical tools, are clearly needed to develop fully effective latency reversing agents (LRAs) for use alone or in combination towards an HIV cure. The overarching objectives of this proposal are to apply genetic, biochemical, and chemical biology approaches to cellular models of latency and HIV+ donor-derived samples to i) define the role of the Polycomb Repressive Complexes, PRC1 and PRC2, in HIV latency and ii) understand the effect of substance use on Polycomb- mediated HIV latency. PRC1 and PRC2 are critical regulators of gene silencing through the installation and recognition of the repressive H3K27me3 post-translational modification (PTM), and hence, are well poised to make a significant contribution to HIV latency. Our preliminary data suggests that components of both PRC1 and PRC2 that have not yet been implicated in the maintenance of HIV latency, as well as Polycomb-associated proteins, are key regulators of latency and novel targets for latency reversal. Additionally, drugs of abuse have been shown to induce changes in epigenetic modifications, including histone methylation, and in turn could significantly impact the epigenetic profiles of resting CD4+ T-cells from HIV-infected drug abusers. Therefore, we also aim to explore the effect of substance abuse on Polycomb function in resting CD4+ T-cells, and the influence of such environmental factors on the establishment and maintenance of HIV latency.